Electric space heater



Nov. 21, 1950 BOXRUD ELECTRIC SPACE HEATER 2 Sheets-Sheet 1 Filed Jan. 1, 1945 Alf M. Boxrud Nov. 21, 1950 A. M. BOXRUD ELECTRIC SPACE HEATER 2 Sheets-Sheet 2 Filed Jan. 1, 1945 mmmm up w p njj w Alf 'Boxrud Patented Nov. 21, 1950 UNITED STATES PATENT OFFICE ELECTRIC SPACE HEATER Alf M. Boxrud, Minneapolis, Minn.

Application January 1, 1945, Serial No. 570,932

3 Claims.

My invention relates to electric space heaters and particularly to the heating elements thereof.

An object of the invention resides in providing an electric heating element which can be constructed of simple and inexpensive materials and without molding or machining of the materials.

An object of the invention resides in providing a heating element in which no hum occurs when the element is energized by alternating current.

An object of the invention resides in constructing each heating element with a plate-like support and having oppositely disposed free edges and in applying to the edges of the support strips of insulating material of a soft compressible nature.

Another object of the invention resides in winding about the support an elongated conductor and in causing said conductor to become imbedded in said strips of insulating material, whereby the convolutions of the conductor are held in spaced relation without the notching or machining of the edges of the support.

Another object of the invention resides in providing a heating element in which an appreciable length of conductor may be confined to a relatively small space so as to economize in the area of the support employed.

A still further object 01 the invention resides in providing a heating element in which the conduetor projects laterally outwardly from the support so that the fluid passing along the su port is more readily brought in contact with the heating element, to insure a maximum transfer of heat from the element to the fluid.

A still. further object of the invention resides in constructing the conductor with a series of undulations each comprising legs extending in opposite directions and connecting portions therebetween.

Another object of the invention resides in cansing the undulations to extend substantially in a plane transverse with respect to the surface of the support.

A feature of the invention residesin arranging alternate undulations in diverging relationship so that the connecting portions thereof are staggered with relation to one another to prevent tilting of the conductor with reference to the support.

Other objects of the invention reside in the novel combination and arrangement of parts and in the details of construction hereinafter illustrated and/or described.

In the drawings:

Fig. 1 is a perspective view of a space heater illustrating an embodiment of my invention.

Fig. 2 is an elevational sectional view taken on line 2-2 of Fig. 1 and drawn to a greater scale. I

Fig. 3 is a cross-sectional view taken on line 33 of Fig. 2.

Fig. 4 is a fragmentary elevational sectional view similar to Fig. 2 illustrating a modification of the invention.

Fig. 5 is a cross sectional view taken on line 5-5 of Fig. 4.

Fig. 6 is a view similar to Fig. 4 of still another form of the invention.

Fig. '7 is a cross sectional view taken on line 1-1 of Fig. 6.

My invention comprises a case H] in which is disposed a number of heating elements ll, l2 and I3. These heating elements are arranged in spaced relation within the case and permit of the circulation of air past the same and through the case. Since all these heating elements are identical in construction, only the heating element l2 and the case ID will be described in detail.

The case I0 consists of side walls It and end walls l5 connected together by means of corner pieces I6. The case M is open at the bottom, being covered by means of a wire screen I! to protect the heating elements H, l2 and I3. This screen is attached to a flange [8 formed on the walls l4 and IS. The case In rests on legs is which are attached to the walls It and I5 and by means of which the case is raised above the surface on which the heater rests, so that air may enter through the screen [1 and pass through the case proper and along the heating elements ll, l2 and i3. The top of the case is also open and is covered by a reticulate member 2| which is secured to the upper edges of the Walls l4 and to end members 22 mounted on the end walls l5. It will thus be readily comprehended that air will enter the case through screen l'l, pass the heating elements ll,- [2 and i3 and leave the case through the reticulate member 2|.

The heating element 12 consists of a platelike support '23 constructed of insulating material such as asbestos board or some other similar material. For the purpose, I have found that a board consisting of Portland cement and asbestos forms an excellent material. The supports 23 of the heating elements H, I! and I3 are supported by means or upper and lower rack bars 24 and 25. These rack bars are spot-welded or otherwise secured to the end walls is of the case In and are provided with offset facing flanges 26 and 27. These flanges have notches 28 out in the same for the reception of the ends of the supports 23. One such notch is shown in Fig. 3 where the lower portion of the heating element H of the heater has been cut to show the same. The supports 23 extend up to the end wals '25 and by means of this construction, said supports are held in proper position with reference to the interior of the case forming vertically extending passageways 3|, 32, 33 and 34 extending along said heating elements on opposite sides thereof.

Arranged on the support 23 is an elongated conductor 35 which is preferablyconstructed'of suitable resistance wire and which is bent at spaced intervals to form spaced undulations designated by the reference numeral Each undulation comprises two legs 58 and 39 extending in-opposite directions'which are connected together by means of connecting portions 40 and 4|. The undulations may be arranged in-a common plane and when applied to the support 23, project outwardly therefrom. Due to the legs of the undulations extending in op: posite directions, hum in the heater is entirely eliminated.

For attaching the convolutions of the conductor 35 to the support 23, two strips 42 and as of asbestos paper or some other similar material is employed which is laid over the marginal portions 44 and 45 of the support 23. The conduc tor 35 is attached to the support by slipping certain of the undulations 36a and 3519 over the insulating strips 42 and 43 and in opening up connecting portions Md of certain conductors adjacent the undulations 33a and 35b sufliciently to cause the intervening undulations to extend outwardly from thesupport 23 as shown in Fig. 3. By,means of this construction, the conductor merely contacts the strips t2 and s3 and is practically free from the support 23 throughout the remainder of its extent excepting where the connecting portions ll contact the same. The undulations 3&1 and 35b become imhedded in the relatively soft insulating paper and are thus held in rigid spaced relation with respect to the support. The ends of the conductors are attached to suitable terminals such as indicated at whereby suitable connections may be made to a source of electrical energy. It will be noted that the undulations 36 extend well into the air passageways Si, 32, 33 and 34, so that rapid transfer of heat from the conductor to the flowing air is procured.

In Figs; 4 and 5, I have shown a modification of the invention in which the undulations are positively maintained in properly extended posi tion. Due to the fact that the construction is similar to that shown in Figs. 2 and 3, the description of the corresponding parts will not be repeated, but will be'desi nated by similar reference characters-to which the prefix 1 has been added. For the purpose of explanation, alternate undulations of this modification are indicated by the reference characters I 35 and 131. In this form of the invention, the only difference residesin the fact that undulations I35 are bent angularly with respect to the undulations I37, the bends occurring at the connecting portions 140 of said conductor. This causes the connecting portions MI to engage the conductor at laterally spaced localities so*that tilt-- provide exceptionally great heat transfer.

ing or movement of the conductor out of their transverse positions is prevented.

In Figs. 6 and '7, still another form of the invention is shown. In this form of the invention, like parts will be designated by the same reference characters with the prefix 2 added thereto. In this form of the invention, legs 238 and 238 are bent angularly at the centers of the same as designated at 25!. This causes the opposed connecting portions 240 and 241 to engage the support 23 at laterally spaced localities. By means of this construction, the conductor is supported in much the same manner as that shown in Figs. 4 and 5.

While Ihave shown the undulations as projecting outwardly from the support, it can readily be comprehended that said undulations may be disposed in the plane of the support.

The advantage of my invention are manifest. An extremely simple and practical construction islprovided whereby: a considerable length of conductor may be installed in a relativelysmall space. The conductor is more or less rigid and extends into the air conducting space so as to With my invention. certain of the undulations may be used for attaching the conductor to the support. By the employment of. the insulating strips at the upper and lower edges of the supports, the

conductors are held in spaced relation without necessity of notching or otherwise fabricating the ends of the supportsthus greatly simplifying the manufacture ofth'e heater.

Changes in the specific form of my invention,

as herein described, may be made within the outwardly from said surface, the parts of the bends of the legs on one side of said conductor lying in one longitudinal plane and the parts of the bends of the legs on the other side of the conductor lying in another longitudinal plane, said planes interse"ting and forming an angle with one another and with said suppcrt.

2. An electric heating element comprising a substantially planiform support, a resistor car ried by the support and comprising an elongated undulated conductor, the undulations of said conductor being arranged with the nodes of the undulations dis osed in a straight line spaced from and parallel to the surface of the support and with the portions of the undulations to the sides of the nodes lying in intersecting planes, the crests of the undulations engaging the support along spaced parallel lines.

3. An electric heating element comprising a,

U-shaped bends disposed at ,the other side. of.

the resistor and transverse'inverted' V-shaped 5 bends connecting the alternate bends on opposite sides of the resistor, the U-shaped bends 1ying on one side of the resistor being disposed in one plane and the U-shaped bends at the other side of the resistor lying in another plane, said planes intersecting one another at an angle determined by the angle 01 the V-shaped bends, the outermost portions of the U-shaped bends engaging the planiform support to space the major portion of the resistor therefrom.

ALF M. BOXRUD.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number 15 178,042 196,480

6 UNITED STATES PATENTS Name Date Gutmann Jan. 26, 1892 Brown et a1. May 27, 1902 Dale et a1. May 12, 1914 Lillianbridge June 14, 1914 Mansbridge Oct. 5, 1915 Louthan Oct, 18, 1927 Apple July 11, 1933 Schonfeld Aug. 8, 1933 Mucher Apr. 4, 1939 FOREIGN PATENTS Country Date Switzerland Sept. 16, 1935 Great Britain Apr. 26, 1923 

